DESCRIPTION (applicant's abstract): Recent molecular and genetic studies indicate that a neuropeptide Y (NPY) mediated signaling pathway, which is conserved among animals including worms and humans, is involved in regulating feeding behavior. However, the mechanism for its regulation is not understood. The long term goal of this proposal is to understand the role of Drosophila neuropeptide F(NPF), a human NPY homolog, in modulating feeding behavior, the underlying mechanism(s), and its functional relationship to vertebrate neuropeptide Y family molecules. Drosophila is the only invertebrate model organism where homologs of NPY and its receptors have been identified. Using whole mount in situ RNA hybridization and immunocytochemistry, we showed that dNPF is expressed in both CNS and gut In larval CNS, dNPFergic neurons of the brain innervate subesophageal, thoracic, and abdominal ganglia, and may thereby act as neurotransmitters for mediating brain control of feeding behavior. We also found that gustatory stimulation by sugars induces dNPF expression in two additional neurons of larval subesophageal ganglion. The expression remains strong long after sugar withdrawl, implicating dNPF in mediating carbohydrate conditioning of fly CNS. The dNPF midgut expression is enhanced by food uptake, and reduced by starvation. One of the putative dNPF receptors is expressed in larval gut, brain and possibly salivary glands. Thus, dNPF may also function as a gut hormone that coordinates feeding associated activities in diverse tissues. In this application, we propose to directly test the specific roles of dNPF in transgenic flies by addressing the following specific aims: 1) Constructing gain-of-function transgenic Drosophila larvae through controlled ectopic dNPF expression and analyzing their feeding behaviors; 2) Cloning and characterization of cis regulatory elements of dNPF using UAStauGFP reporter system; 3) constructing loss-of-function transgenic larvae through targeted functional knockout of dNPF and determining the specific roles of brain, subesophageal ganglion and midgut dNPF in feeding behavior. These studies should provide general insights into the signaling mechanism for feeding regulation in invertebrates as well as higher animals including humans.